do not add alias when command not found

bashrc

@@ -146,10 +146,10 @@ null type e3em && alias e3=e3em
 #alias dirs="dirs -v -l | \grep -v \$(printf '%s$' \$PWD)"
 alias po=popd
 alias pu=pushd
-alias sudo="sudo "              # use aliases through sudo
-alias sudoe="sudoedit"
-alias halt="sudo halt"
-alias reboot="sudo reboot"
+null type sudo && alias sudo="sudo "              # use aliases through sudo
+null type sudoedit && alias sudoe="sudoedit"
+null type halt && alias halt="sudo halt"
+null type reboot && alias reboot="sudo reboot"
 null type dbus-send && {
     alias suspend="dbus-send --system --print-reply --dest=org.freedesktop.UPower \
     /org/freedesktop/UPower org.freedesktop.UPower.Suspend"

emacs.el

@@ -360,13 +360,15 @@ found, otherwise returns nil."
                            trailing     ; trailing blanks
                            newline      ; newlines
                            newline-mark ; use display table for newline
+                           tab-mark
                            empty        ; empty lines at beg or end of buffer
                            lines-tail  ; lines over 80
                            ))
   ;; (setq whitespace-newline 'font-lock-comment-face)
   (add-to-list 'whitespace-display-mappings
-               `(newline-mark ?\n ,(vconcat "$\n"))
-               )
+               `(newline-mark ?\n ,(vconcat "$\n")))
+  (add-to-list 'whitespace-display-mappings ; not work
+               `(tab-mark ?\t ,(vconcat "^I\t")))
   (global-whitespace-mode t)
   (when (eq (display-color-cells)
             256)